Process for the preparation of large surface area, finely divided precipitated calcium carbonate and filled polymeric compositions of matter containing said calcium carbonate

ABSTRACT

This invention concerns a process for the preparation of large surface area, finely divided precipitated calcium carbonate which comprises introducing carbon dioxide into an aqueous slurry of greater than about five weight percent calcium hydroxide containing an anionic organopolyphosphonate polyelectrolyte, starting the introduction at a temperature above about 7° C. and below about 18° C., continuing the introduction until calcite precipitation is substantially complete and adding a quantity of polybasic acid to the slurry in an amount greater than about 0.3% by weight of the precipitated calcium carbonate. This invention also concerns said large surface area, finely divided precipitated calcium carbonate which has been coated with a fatty acid derivative and polymeric compositions which contain such coated calcium carbonate.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 204,057, filed6-7-88, now Pat. No. 4,927,618, issued 5-22-90, which is acontinuation-in-part of application Ser. No. 123,037, filed Nov. 19,1987, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns precipitated calcium carbonate having a largesurface area. More specifically, it concerns a novel process forpreparing finely divided precipitated calcium carbonate having a largesurface area and high purity. Additionally, this invention relates tolarge surface area, finely divided precipitated calcium carbonate coatedwith fatty acid derivatives. Further, this invention relates to filledpolymeric compositions of matter wherein the filler comprises calciumcarbonate of this invention alone or in addition to other fillers knownin the art.

2. General Background

A process for precipitating calcium carbonate (calcite) by thecarbonation of an aqueous lime slurry in the presence of certainorganophosphorous compounds is disclosed in U.S. Pat. No. 4,367,207. Theprocess disclosed in that patent concludes by the treatment of thecarbonated slurry with sufficient polybasic acid to essentiallyneutralize any unreacted calcium hydroxide present. U.S. Pat. No.4,367,207 teaches the production of calcium carbonate of an averageparticle size diameter of about 0.01 to 0.03 microns.

A process for producing uniform grain size calcium carbonate by reactingcalcium carbonate having an average particle diameter of not more than20 microns with acidic gas is disclosed in West German Pat. No.2,741,427. That process, however, requires that the acid gas bedehydrated before use as otherwise the calcium carbonate particles willjoin together and form lumps or aggregates.

Polyvinylchloride is a transparent polymer which becomes opaque whencalcium carbonate having a small specific surface area is added asfiller. In order for dispersion of calcium carbonate inpolyvinylchloride polymers to occur, the calcium carbonate must becoated with a fatty acid derivative such as a salt of stearic acid. Evencoated small specific surface area calcium carbonate imparts a largedegree of opacity to polyvinylchloride polymers.

SUMMARY OF THE INVENTION

The present invention concerns a process for the preparation of largesurface area, finely divided precipitated calcium carbonate whichcomprises introducing carbon dioxide into an aqueous slurry of greaterthan about five weight percent calcium hydroxide containing an anionicorganopolyphosphonate polyelectrolyte from about 0.02 to about 1.0weight percent based on the calcium carbonate equivalent of thehydroxide, preferably in the amount of from about 0.05 to 0.5 weightpercent, starting the introduction at a temperature above about 7° C.and below about 18° C., preferably above about 10° C. and below 15° C.,continuing the introduction until calcite precipitation is substantiallycomplete and adding a quantity of polybasic acid to the slurry in anamount greater than about 0.3% by weight of the precipitated calciumcarbonate, preferably in an amount of from about 1% to about 3% byweight of the precipitated calcium carbonate.

This invention also concerns precipitated calcium carbonate having largesurface area produced according to the process described above which hasbeen coated with a fatty acid derivative and the incorporation of such afatty acid derivative coated precipitated calcium carbonate as a fillerin polymeric compositions, preferably polyvinylchloride. Suchpolyvinylchloride polymer compositions filled with the fatty acidderivative coated precipitated calcium carbonate of this invention haveenhanced properties of decreased shear stress, increased impact strengthand an increased output level of polymer per unit of energy consumptionwithout significantly sacrificing the transparency of the composition.Preferably, the fatty acid derivative used to coat the calcium carbonateto be used as filler in polyvinylchloride is ammonium or sodiumstearate.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph of the notched Izod impact strength of medium lowmolecular weight polyvinylchloride polymers as a function of variouslevels of two different sodium stearate coated precipitated calciumcarbonate preparations. One calcium carbonate preparation had a specificsurface area before coating of 22 m² /g and the other had a specificsurface area before coating of 85 m² /g . All of the compositionscontained 5 phr (parts per hundred resin) of KM-680 impact modifier.

FIG. 2 is a graph of the notched Izod impact strength of medium lowmolecular weight polyvinylchloride polymers as a function of variouslevels of KM-680 impact modifier in the presence of (i) no calciumcarbonate , (ii) 4 phr calcium carbonate (85 m² /g, sodium stearatecoated) or (iii) 6 phr calcium carbonate (85 m² /g, sodium stearatecoated) Δ.

DETAILED DESCRIPTION OF THE INVENTION

The initial part of the process of this invention, namely, theprecipitation of calcium carbonate by introducing carbon dioxide into anaqueous slurry containing anionic organopolyphosphonate polyelectrolytestarting at from about 7° C. to below about 18° C., is fully describedin U.S. Pat. No. 4,367,207, the teachings of which are incorporatedherein by reference. In practicing the process of U.S. Pat. No.4,367,207 it was found that the amount of polybasic acid required toneutralize the remaining unreacted calcium hydroxide was generally equalto about 0.3% by weight based upon the amount of precipitated calciumcarbonate and the resulting precipitated calcium carbonate had aspecific surface area less than about 60 m² /g. The instant invention,however, departs from the process of that patent with the addition ofpolybasic acid in an amount greater than about 0.3% by weight based uponthe amount of precipitated calcium carbonate. By adding the additionalpolybasic acid the resulting finely divided precipitated calciumcarbonate has a larger surface area and other useful properties as morefully described hereinbelow.

Suitable polybasic acids for use in the process of this inventioninclude maleic, malic, tartaric, citric, malonic, phthalic, boric,sulfuric, aspartic, sulfurous, oxalic, glutaric and phosphoric acids.Preferably, the polybasic acid used in the process is phosphoric acid.

The anionic organopolyphosphonate polyelectrolyte employed in theprocess of this invention is in the amount of from about 0.02 to 1.0weight percent based on the calcium carbonate equivalent of thehydroxide contained in the reaction mixture and, preferably, in anamount of from 0.05 to 0.5 weight percent.

Preferably, the polybasic acid is phosphoric acid in an amount of fromabout 1.0% to about 3.0% by weight of the precipitated calciumcarbonate. Still more preferably, the anionic organopolyphosphonatepolyelectrolyte employed in the process of this invention is(2-hydroxyethylimino)bis(methylene)bis phosphonic acid and thetemperature at which the introduction of carbon dioxide is started isabove about 10° C. and below about 15° C.

The use of an increased level of polybasic acid after precipitation ofthe calcium carbonate affects the aging/crystal growth phenomenon knownto occur in calcium carbonate particles in the wet state. The effect,which is the retardation of the aging process, results in precipitatedcalcium carbonate having a larger surface area in the resulting driedmaterial.

The precipitated calcium carbonate produced by the novel process of thisinvention can be further treated with a fatty acid derivative coating,preferably a stearic acid derivative, by methods well known to thoseskilled in the art. Such coated precipitated calcium carbonate can thenbe used as a filler or co-filler in a variety of polymeric compositions.Preferably, the precipitated calcium carbonate used for such fillers inpolyvinylchloride polymer compositions has an average specific surfacearea of from about 75 m² /g to about 85 m² /g and has been coated with astearic acid derivative. Precipitated calcium carbonate having a smallerspecific surface area results in significantly less transparency infilled polyvinylchloride polymers while a larger specific surface arearesults in less dispersion of the calcium carbonate in thepolyvinylchloride polymer. It has been found that precipitated calciumcarbonate having a specific surface area of about 100 m² /g or greateris not suitable for use as a filler for polyvinylchloride.

The use of stearic acid derivative coated precipitated calcium carbonateproduced according to the process of this invention as a filler orco-filler in polyvinylchloride polymer compositions results in theproduction of novel compositions with increased impact strength atreduced impact modifier levels, increased shear strength and increasedoutput of polymer per unit of energy consumption during manufacturewithout significantly reducing the transparency of the composition.Preferably, the precipitated calcium carbonate employed in suchcompositions is coated with a stearic acid derivative containing theequivalent of about 10% by weight of stearic acid compared to theprecipitated calcium carbonate and has an average specific surface areabefore coating of from about 75 m² /g to about 85 m² /g. Still morepreferably, the stearic acid derivative is ammonium stearate or sodiumstearate. The stearic acid derivative coated precipitated calciumcarbonate can be employed as a filler in such compositions at levels upto about 10 phr (parts per hundred resin). Preferably, such calciumcarbonate filler is used at levels from about 4 to about 6 phr. Suchcompositions can also contain stabilizers, process aids, lubricants andtoner as well as impact modifier, all of which are well known to thoseskilled in the art. However, the level of impact modifier employed toachieve satisfactory impact strength in such compositions is reduced bythe addition of the coated precipitated calcium carbonate and theresulting polymer does not suffer from any significant reduction intransparency. The compounding and blending of such compositions will bereadily apparent to those skilled in the art enabled by the disclosureof this invention.

The filled polyvinylchloride polymers of this invention are suitable foruse in the manufacture of bottles, light panels, greenhouse panels,privacy fences and the like.

Other filled polymeric compositions can be made employing the largesurface area, finely divided precipitated calcium carbonate produced bythe process of this invention by those skilled in the art, enabled bythe teachings of this invention. For example, polymers of similarrefractive index to polyvinylchloride such as low density polyethylenescan be so filled. It is to be noted, however, that polystyrene filledwith the finely divided precipitated calcium carbonate of this inventionsuffers a loss to its physical properties although its clarity is lessaffected.

Still other uses for the precipitated calcium carbonate producedaccording to the process of this invention exist and will be apparent tothose skilled in the art enabled by this disclosure.

The following Examples serve to illustrate the present invention and arenot to be construed to limit the invention in any way to the specificembodiments contained therein.

EXAMPLE 1

The following calcium carbonate precipitation was conducted in a 30liter stainless steel reactor equipped with a cooling jacket, anagitator having two pitched-blade turbine impellers, a stainless steelcarbonation tube to direct a carbon dioxide gas stream to the impellerand a probe for monitoring the pH of the suspension.

A calcium hydroxide slurry was prepared by rapidly adding 1,550 g ofpulverized reactive lime having an approximately 93% available calciumoxide content to 7.75 liters of water at 50° C. contained in the 30liter reactor agitated at 400 rpm. After 10 minutes the slake limeslurry was cooled from its final temperature of 82° C. to 13° C.

An amount of active (2-hydroxyethylimino) bis(methylene)bis phosphonicacid (Wayplex® 61-A, Philip A. Hunt Chemical Corp.) equivalent to 0.05%by weight of the calcium carbonate equivalent of the calcium hydroxideslurry was added to the slaked lime slurry. The slurry was diluted with15.50 liters of water to give a final calcium hydroxide concentration of7.68%. The slaked lime slurry was adjusted to 13° C., the agitation rateset at 800 rpm, and the slurry was carbonated by passing a 28 volumepercent carbon dioxide in air mixture at 85 liters/minute through theslurry. The batch was carbonated over a 31 minute period to a pH of 8.0.The batch was cooled throughout the carbonation during which time thetemperature increased to 19° C. The carbonated slurry was then treatedwith 60.5 g of 85% phosphoric acid diluted 1:1 with water, representing2.0% phosphoric acid based on the calcium carbonate content of theslurry. The slurry pH dropped to 6.9 after the phosphoric acid addition.The slurry was then passed through a 325 mesh screen to remove the gritpresent in the lime and dewatered on a vacuum filter. The filter cakewas dried overnight at 110° C. to yield precipitated calcium carbonatehaving a specific surface area of 85 m² /g. The surface area wasdetermined by outgassing a sample of the precipitated calcium carbonateof known weight in nitrogen at 275° C. for 45 minutes, then measuringthe surface area by the single point BET nitrogen adsorption methodusing Micromeritics Model 2200 Surface Area Analyzer (Micromeritics,Norcross, Ga.) according to the procedure described in MicromeriticsInstruction Manual (Catalog No. 220/00000/0X), dated Oct. 8, 1979. Thespecific surface area was then calculated by dividing the surface areaso determined by the weight of the sample and is expressed as m² /g.

EXAMPLE 2

Precipitated calcium carbonate was prepared using the same equipment andslaking and carbonation procedures of Example 1 with the followingdifferences. The starting carbonation temperature was 15° C. and rose to18° C. after carbonating for 31 minutes to a pH of 8.0. The productslurry was then treated with 36.3 g of 85% phosphoric acid representing1.2% phosphoric acid based on the calcium carbonate content of theslurry. The final dried product from this Example had a specific surfacearea of 74 m² /g.

EXAMPLE 3

Precipitated calcium carbonate was prepared following the slaking andcarbonation procedures of Example 2 with the following exceptions. Thecalcium hydroxide concentration was 11.2%, the Wayplex® 61-A amount was0.25% on a calcium carbonate basis and the starting carbonationtemperature was 14° C., rising to 15° C. at the end of carbonation. Thecarbonated slurry was treated with 30.2 g of 85% phosphoric acid or 1.0%phosphoric acid based on the calcium carbonate content of the slurry.The final dried product had a specific surface area of 82 m² /g.

EXAMPLE 4

Precipitated calcium carbonate was prepared according to the proceduresof Example 1 with the following variations. The calcium hydroxideconcentration at the beginning of carbonation was 9.45%, the temperaturewas 12° C. rising to 18° C. at the end of carbonation. An amount ofphosphoric acid corresponding to 1.2% on a calcium carbonate basis wasadded to the carbonated slurry. The final dried calcium carbonateproduct had a specific surface area of 77 m² /g.

EXAMPLE 5

Precipitated calcium carbonate was prepared according to the proceduresof Example 1 with the following differences. The calcium hydroxideconcentration was 11.2% and 1.6% phosphoric acid on a calcium carbonatebasis was added to the final carbonated slurry. The final dried calciumcarbonate had a specific surface area of 85 m² /g.

EXAMPLE 6

Using the equipment and procedures of Example 1, a series ofprecipitated calcium carbonate preparations were prepared using variouslevels of phosphoric acid and with the following variations. TheWayplex® 61-A amount was 0.25% on a calcium carbonate basis and thestarting carbonation temperature was 14° C. The carbonated slurry wasreacted with phosphoric acid at various levels. The surface area of theprecipitated calcium carbonate so produced was measured as described inExample 1. The results, which demonstrate the effect of various levelsof phosphoric acid on the specific surface area of precipitated calciumcarbonate so produced, are contained in Table I below. As Table I shows,the specific surface area of the precipitated calcium carbonateincreases as the amount of phosphoric acid increases.

                  TABLE I                                                         ______________________________________                                        Effect of Various Phosphoric Acid Levels                                      on Specific Surface Area of Precipitated                                      Calcium Carbonate                                                                                       Specific                                                                      Surface Area                                        Example No.  H.sub.3 PO.sub.4 (wt. %)*                                                                  (m.sub.2 /g)                                        ______________________________________                                        6A           0.0          47.5                                                6B           0.75         71.9                                                6C           1.0          80.6                                                6D           1.5          89.8                                                6E           2.0          92.3                                                6F           3.0          96.9                                                6G           4.0          101.4                                               ______________________________________                                         *wt. % is based on the calcium carbonate content of the slurry.          

EXAMPLE 7

Precipitated calcium carbonate slurry prepared according to theprocedure of Example 5 up to and including the 325 mesh screening stepwas reacted with a surface treating agent in the following manner.

Stearic acid was liquified by adding 244 g of commercial triple-pressedstearic acid to 1950 ml of water heated to 75°-80° C. under mildagitation. To the stearic acid emulsion was added 151 g of a 25% sodiumhydroxide solution to prepare a sodium stearate solution. Fifteen litersof slurry containing 2200 g of calcium carbonate was agitated and heatedto 80° C. in a 30 liter vessel. The sodium stearate solution was thenslowly added over about 5 minutes to the well-agitated calcium carbonatesuspension. The suspension was maintained at 80°-85° C. for one hour.The hot, coated calcium carbonate slurry was filtered, dried at 110° C.and pulverized to yield a fine powder. Analysis of the product showed itto contain 10% by weight stearic acid equivalent.

EXAMPLE 8

Surface coated precipitated calcium carbonate was prepared according tothe procedure of Example 7 except for a modification in the preparationof the stearate coating emulsion. In this case the stearic acid emulsionwas neutralized with an excess of ammonium hydroxide rather than sodiumhydroxide.

Thus, an ammonium stearate emulsion was prepared by adding 47 g of 29%ammonium hydroxide solution to 159 g of triple-pressed stearic acidcontained in 1.5 liters of water at 80° C. under mild agitation. Theammonium stearate emulsion was then added over about a five minuteperiod to 12 liters of an agitated aqueous suspension containing 1427 gof calcium carbonate at 80° C. in a 30 liter vessel. The suspension washeld at 80°-85° C. under agitation for one hour. The hot, coated calciumcarbonate slurry was filtered, dried at 110° C. and pulverized to yielda powder containing 10% by weight stearic acid equivalent.

EXAMPLE 9

Polyvinylchloride formulations were prepared using a medium lowmolecular weight polyvinylchloride and a basic formulation suitable forbottle applications with 5 phr of impact modifier and various levels of10% sodium stearate coated precipitated calcium carbonate having aspecific surface area before coating of either 22 m² /g or 85 m² /g. Thebasic formulation used was as follows:

    ______________________________________                                                            Parts                                                     ______________________________________                                        PVC Resin (K52-55).sub.a                                                                            100                                                     Tin Stabilizer (octyl) [M&T 813].sup.b                                                              0.5                                                     Tin Stabilizer (octyl) [M&T 831].sup.b                                                              1.5                                                     Impact Modifier KM-680.sup.c                                                                        5.0                                                     Process Aid (Acrylic) [M&T P550].sup.b                                                              1.2                                                     Process Aid (Acrylic) [M&T P700].sup.b                                                              1.2                                                     Lubricant (External) [HOB 7107].sup.d                                                               0.7                                                     Lubricant (Internal) [HOB 7111].sup.d                                                               0.4                                                     Toner (Blue).sup.e     0.005                                                  Calcium Carbonate     various                                                 (Sodium Stearate Coated)                                                      ______________________________________                                         .sup.a Georgia Gulf Corporation, Plaquemine, Louisiana                        .sup.b M&T Chemicals, Inc.                                                    .sup.c Rohm & Haas, Philadelphia, Pennsylvania                                .sup.d Henkel Chemical                                                        .sup.e H. Kohnstamm                                                      

The above formulations, which contained various levels of sodiumstearate coated calcium carbonate of different specific surface area,were compounded using a Farrell Model BR Banbury mixer (Farrell, Inc.,Ansonia, Conn.). The dry blends (1.8 kg each) were mixed at a motorspeed of 230 rpm and a ram air pressure of 20 psi (1.4 kg/cm²) untilcomplete fusion was obtained (about 330° F. (165.6° C.)). The fusedplastic was sheared for an additional thirty (30) seconds at a motorspeed of 116 rpm and then discharged onto a hot two roll mill (300° F.(148.9° C.)) to form a 1/4" (6.35 mm) thick sheet. The sheet was cutinto pieces about six inches (15.2 cm) square and granulated when cool.The granules were injection molded into standard ASTM test pieces in anArburg Allrounder Model 320-210-750 injection molding machine (PolymerMachinery, Inc., Berlin, Conn.) outfitted with a 30 mm diameter screwhaving a length to diameter ratio of 23.5:1, a compression ratio of1.8:1 and having a smear tip. The injection unit temperature settingsfrom feed section to nozzle were 300° F. (148.9° C.), 330° F. (165.6°C.), 350° F. (176.7° C.) and 380° F. (193.3° C.). The mold temperaturewas 90° F., the screw speed was 85 rpm and the back pressure was lessthan 100 psi (7 kg/cm²). Injection pressure was adjusted to yield acavity pressure of 5000 psi (351.5 kg/cm²).

Ten molded flex bars for each formulation were conditioned for at least48 hours at 65% relative humidity and 72° F. (22.2° C.), cut and notchedaccording to ASTM procedure D-256, Method A. Using the ASTM D-256 testprocedure, the notched Izod was determined for the formulationsdescribed above. The results are shown in FIG. 1.

The precipitated calcium carbonate of this invention when coated withsodium stearate and used in formulations of polyvinylchloride enhancedthe notched Izod impact properties of the polymer to a greater extentand at a lower level than did the sodium stearate coated precipitatedcalcium carbonate having a specific surface area of 22 m² /g.

EXAMPLE 10

Various formulations of medium low molecular weight polyvinylchloridewere prepared according to the procedure of Example 9 except that theformulations did not contain impact modifier and the formulationscontained 5 phr of a specific coated precipitated calcium carbonate. Theprocess of blending was the same and the blends, after fusion andshearing were discharged onto a hot two roll mill (300° F. (148.9° C.))to form a 30±2 mil thick sheet. One formulation contained sodiumstearate coated precipitated calcium carbonate (22 m² /g before coating)produced according to U.S. Pat. No. 4,367,207. Another formulationcontained sodium stearate coated precipitated calcium carbonate (85 m²/g before coating) produced according to this invention. A thirdformulation contained ammonium stearate coated precipitated calciumcarbonate (85 m² /g before coating) produced according to thisinvention. All of the coated precipitated calcium carbonates containedabout 10% by weight of stearic acid equivalent.

Samples from the sheets so produced were assayed for opacity accordingto the procedures described in ASTM-D2805-85 and the results are shownbelow in Table II.

                  TABLE II                                                        ______________________________________                                        Opacity of Unfilled and Filled Medium Low                                     Molecular Weight Polyvinylchloride Polymer Sheets                             Filler              Opacity                                                   ______________________________________                                        None                10.3%                                                     Sodium Stearate coated                                                                            28.3%                                                     PCC* (22 m.sup.2 /g)                                                          Sodium Stearate coated                                                                            19.9%                                                     PCC of this invention                                                         (85 m.sup.2 /g)                                                               Ammonium Stearate coated                                                                          15.8%                                                     PCC of this invention                                                         (85 m.sup.2 /g)                                                               ______________________________________                                         *PCC = precipitated calcium carbonate.                                   

EXAMPLE 11

Using the procedure described in Example 9, various polyvinylchlorideformulations were prepared with the following variations:

    ______________________________________                                                              CaCO.sub.3 (85 m.sup.2 /g                                                     before coating)                                                      KM-680   (10% sodium                                                          Modifier stearate coated)                                        No.          phr      phr                                                     ______________________________________                                        11A          8        0                                                       11B          9        0                                                       11C          10       0                                                       11D          12       0                                                       11E          8        4                                                       11E          9        4                                                       11G          10       4                                                       11H          8        6                                                       ______________________________________                                    

The formulations were blended, molded and tested for notched Izod impactstrength as described in Example 9. The resulting notched Izod impactvalues for the various polymers are shown in FIG. 2. The addition of 85m² /g CaCO₃ coated with 10% sodium stearate significantly increased thenotched Izod impact strength of the polymers at reduced levels of impactmodifier.

EXAMPLE 12

The effect of varying levels of impact modifier and calcium carbonatefiller on polyvinylchloride polymer output was examined according to thefollowing method. Various compositions of polyvinylchloride wereprepared according to the process of Example 9 except that the level ofKM-680 impact modifier and calcium carbonate were varied. Theprecipitated calcium carbonate employed had an average specific surfacearea of 85 m² /g and was coated with sodium stearate. The polymercompositions were blended as described in Example 9 and then extrudedfrom a Leistritz Extruder at 16-17 Amps under a die pressure of 800-900psi (56.2-63.3 kg/cm²). The output from the extruder was measured inpounds per hour (kg per hour) and the results are shown below in TableIII.

                  TABLE III                                                       ______________________________________                                        Effect of Various Impact Modifier and CaCO.sub.3                              (85 m.sup.2 /g) Levels on Extruder Output of                                  Filled Polyvinylchloride Polymer                                                      KM-680                                                                CaCO.sub.3                                                                            Impact Modifier  Output                                               (phr)   (phr)            (lbs/hr) [kg/hr]                                     ______________________________________                                        0       10               21        [9.53]                                     4       10               27       [12.25]                                     4       9                27       [12.25]                                     6       8                26       [11.79]                                     6       7                26       [11.79]                                     ______________________________________                                    

The use of 4 phr of coated precipitated calcium carbonate with either 10or 9 phr of impact modifier resulted in an output increase of more than25%. This, coupled with a reduction in the amount of impact modifierwhich is possible without sacrificing impact strength (see Example 11),results in a composition which has transparency and impact strength andwhich can be produced much more economically.

COMPARATIVE EXAMPLE

Polyvinylchloride formulations were prepared as described in Example 9with the following variations. The impact modifier was used at a levelof 9 phr. Two different preparations of sodium stearate coatedprecipitated calcium carbonate were employed at levels of 2 phr and 4phr. One preparation was precipitated calcium carbonate producedaccording to U.S. Pat. No. 4,367,207 and had a specific surface areabefore coating of 42 m² /g. The other preparation was precipitatedcalcium carbonate produced according to this invention having a specificsurface area before coating of 85 m² /g. Following the blending, moldingand testing procedures of Example 9, the notched Izod values for therespective compositions were determined and are shown in Table IV below.

                  TABLE IV                                                        ______________________________________                                        Notched Izod Values of Polyvinylchloride Polymers                             Containing 9 phr Impact Modifier and 42 m.sup.2 /g or                         85 m.sup.2 /g Precipitated Calcium Carbonate                                  Coated with Sodium Stearate                                                   Specific                                                                      Surface Area                                                                  (m.sup.2 /g)  phr    notched Izod (ft.lb/in)                                  ______________________________________                                        42            2      2.7                                                      4             9.0                                                             85            2      3.1                                                      4             16.8                                                            ______________________________________                                    

The data in Table IV show that the use of precipitated calcium carbonatehaving a specific surface area of 85 m² /g, produced according to theprocess of this invention and coated with sodium stearate as a fillerincreased the impact strength of polyvinylchloride polymers above thatobtained with sodium stearate coated calcium carbonate having a specificsurface area of 42 m² /g produced according to the process of U.S. Pat.No. 4,367,207 at both levels tested.

What is claimed is:
 1. A filled polymeric composition wherein saidfiller comprises precipitated calcium carbonate having a coating thereonderived from a salt of a fatty acid, prepared according to a processwhich comprises introducing carbon dioxide into an aqueous slurry ofcalcium hydroxide containing anionic organopolyphosphonatepolyelectrolyte present in the amount of from about 0.02 to about 1.0weight percent based on the calcium carbonate equivalent of saidhydroxide, the concentration of said hydroxide in said slurry beinggreater than about 5 weight percent, starting said introduction at atemperature above about 7° C. and below about 18° C., continuing saidintroduction until calcium carbonate precipitation is substantiallycomplete, adding a polybasic acid selected from the group consisting ofmaleic, malic, tartaric, citric, malonic, phthalic, boric, sulfuric,aspartic, sulfurous, oxalic, glutaric and phosphoric acids in an amountfrom about 0.75 to about 4.0 weight percent based on the precipitatedcalcium carbonate and reacting the precipitated calcium carbonate with asalt of a fatty acid, with the proviso that when the polymer ispolyvinylchloride, the specific surface area of the calcium carbonate isnot greater than about 100 m² /g.
 2. The filled polymeric compositionaccording to claim 1 wherein the polymeric is polyvinylchloride.
 3. Thefilled polymeric composition according to claim 2 wherein the calciumcarbonate has an average specific surface area of from about 75 m² /g toabout 85 m² /g.
 4. The filled polymeric composition according to claim 3wherein the calcium carbonate is present at from about 4 phr to about 6phr.
 5. The filled polymeric composition according to claim 4 whereinthe salt of a fatty acid is sodium stearate or ammonium stearate.
 6. Afilled polyvinylchloride polymer composition which comprisespolyvinylchloride; about 9 phr of impact modifier; and about 4 phr ofprecipitated calcium carbonate having an average specific surface areaof from about 75 m² /g to about 85 m² /g and having a coating thereonderived from a salt of a fatty acid.
 7. The filled polyvinylchloridepolymer composition according to claim 6 wherein the salt of a fattyacid is ammonium stearate or sodium stearate.